Electrode choice matters more than scientists thought for next-gen light displays
A new study overturns a decade-old assumption that electrode material doesn't affect light-emitting electrochemical cells, a promising low-cost display technology. Researchers found that electrode composition shifts where light is actually generated inside the device—a discovery that could improve performance and cut manufacturing costs for flexible screens and lighting.
Originaltitel: Impact of the electrode material on the performance of light-emitting electrochemical cells
<p>Light-emitting electrochemical cells (LECs) are promising candidates for fully solution-processed lighting applications because they can comprise a single active-material layer and air-stable electrodes. While their performance is often claimed to be independent of the electrode material selection due to the in situ formation of electric double layers (EDLs), we demonstrate conceptually and experimentally that this understanding needs to be modified. Specifically, the exciton generation zone is observed to be affected by the electrode work function. We rationalize this finding by proposing that the ion concentration in the injection-facilitating EDLs depends on the offset between the electrode work function and the respective semiconductor orbital, which in turn influences the number of ions available for electrochemical doping and hence shifts the exciton generation zone. Further, we investigate the effects of the electrode selection on exciton losses to surface plasmon polaritons and discuss the impact of cavity effects on the exciton density. We conclude by showing that we can replicate the measured luminance transients by an optical model which considers these electrode-dependent effects. As such, our findings provide rational design criteria considering the electrode materials, the active-material thickness, and its composition in concert to achieve optimum LEC performance.</p>